Flow batteries, also known as redox flow batteries or redox flow cells, are designed to convert electrical energy into chemical energy that can be stored and later released when there is demand. As an example, a flow battery may be used with a renewable energy system, such as a wind-powered system, to store energy that exceeds consumer demand and later release that energy when there is greater demand. Flow batteries are distinguished from other electro-chemical devices by, inter alia, the use of one or more externally-supplied, liquid electrolyte solutions that include reactants that participate in reversible electrochemical reactions.
A typical flow battery includes a redox flow cell that has a negative electrode and a positive electrode separated by an electrolyte layer, which may include a separator, such as an ion-exchange membrane. The electrodes can be porous carbon materials, such as graphite felts or graphite papers. A negative liquid electrolyte is delivered to the negative electrode and a positive liquid electrolyte is delivered to the positive electrode to drive electrochemically reversible redox reactions. Over time, catalytic performance can decay, particularly at the negative electrode, due to chemical reduction of electrode surface groups, requiring electrode replacement or regeneration.